Magnetic sound recording head



Oct '8, 95 F. BERGMANN 2,809,237

MAGNETIC SOUND RECORDING HEAD Filed Feb. 5, 1951 INVENTOR: FRIEDRICHBERGMANN ATT'YS United States Patent Ofiicc 2,809,237 Patented st. 8,1957 7 2,809,237 MAGNETIC some RECGRDING rman Friedrich Bergmann,Ludwigshafen (Rhine), Germany,

assignor to Badische Aniiin- & Soda-Fahrih Aktiengeselischaft,Ludwigshafen (Rhine), Germany Application February 3, 1951, Serial No.299,258] Claims priority, application Germany February 6, 1950 6 Claims.(Cl. 179-1062) This invention relates to means for the magnetographicrecording of sound.

The magnetic sound recording head hitherto used insound recording andsound reproduction consists of a magnetic core and a wire coiling aroundthe said core. The electric oscillations flowing through the said wirecoiling generate an alternating magnetic field in the vicinity of a slitprovided in the magnetic core and this field imprints itself upon thepermanently magnetisable sound carrier on being led past the said slit.To secure the highest possible efliciency magnetic sound recording headsare fitted with magnetic cores of highly permeable material, as forexample iron-nickel or iron-nickle-copper alloys which are known to havea very high initial permeability. To cut down the eddy losses in themagnetic core during operation, the core is made up of sheets which areinsulated against each other from electricity.

By reason of the high conductivity of the metallic materials hithertoused for making the core, the magnetic sound recording heads aremarkedly dependent as to their magnetic field from the frequency, inparticular are the high frequencies notably affected, since the eddiesin the magnetic core increase in proportion to the square of thefrequency.

I have now found that the disadvantages hitherto inherent in magneticsound recording heads can be substantially obviated by using magneticferrite, instead of the materials listed above, for making the cores ofmagnetic sound recording heads. Examples of ferrites contemplated foruse within the purview of my invention are nickel ferrite, nickel-zincferrite, manganese ferrite and manganese-zinc ferrite. These substancesnot only have high initial permeability but also a very low electricconductivity. They can be used in a compact from as a material formaking magnetic cores, without eddy losses occurring and, as a result,the magnetic field being brought into dependency from the frequency atthe slit provided in the magnet.

According to a preferred embodiment of my invention the magnet cores maybe made by preparing a mixture of 9.4 percent of nickel oxide, 23.8percent of zinc oxide and 66.8 percent of ferric oxide, either byintimately mixing the said oxides or by precipitating them jointly fromtheir respective metal salt solutions, pressing the mixture intosuitably shaped molds, annealing the resulting shaped body at atemperature of between about 1200 and 1300 C. in an atmosphere of oxygenand allowing it to cool down very slowly in this atmosphere. More easeand conveniency in the manufacture of the cores will be afforded bygiving the cores, instead of the standard circular form, a square-barform in crosssection, because the ferrites may be more easily pressedand annealed in this shape. In practical use, three such bars arearranged to form a triangle with a slit being left at one of theintersectional points of the bars. The ends of the bars and the slidingsurface for the recorder band may be suitably shaped by abrasion.

One embodiment of my invention is illustrated in the accompanyingdrawing in which 1 represents the squarebars made of ferrite, 2represents the slit, 3 represents the wire coiling and 4 represents therecorder band.

What I claim is:

1. Magnetic sound recording head having a core consisting exclusively ofmagnetic ferrite.

2. Magnetic sound recording head having a core consisting exclusively'ofmanganese ferrite.

3. Magnetic sound recording head having a core consisting exclusively ofnickel-zinc ferrite.

4. Magnetic sound recording head having a core consisting exclusively ofmanganese-zinc ferrite.

5. Magnetic sound recording head having a core consisting of three barsmade exclusively from ferrite and arranged to form a triangle with aslit being left at one of the intersection points of the bars.

6. A magnetic sound recording head comprising a magnetic core havinglegs separated by a slit, said core including the portions thereofadjacent said slit consisting solely of magnetic ferrite.

References Cited in the file of this patent UNITED STATES PATENTS2,452,529 Snoek Oct. 26, 1948 2,452,530 Snoek Oct. 26, 1948 2,452,531Snoek Oct. 26, 1948 2,493,742 Begun Jan. 10,1950 2,536,260 Burns Jan. 2,1951 2,592,652 Buhrendorf Apr. 15, 1952 FOREIGN PATENTS 274,288Switzerland June 16, 1951

1. MAGNETIC SOUND RECORDING HEAD HAVING A CORE CONSISTING EXCLUSIVELY OFMAGNETIC FERRITE.